From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5D3B7C3A5A7 for ; Wed, 4 Sep 2019 12:52:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2A6E32073F for ; Wed, 4 Sep 2019 12:52:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567601575; bh=XG+z6BHhOmv9W2OyuDcqw63mHyObz78oeswsmfEdF1U=; h=Subject:From:To:Cc:Date:In-Reply-To:References:List-ID:From; b=UkB0Si5sJc08gbYG5d/PPsNQPzGoujz2e0B3ckAgwHsRfjomW2DculZBvs4fcfgQ6 1h8nJBRzE0LMSIw2XhErFNqhgyCLmX/FAcc/iSMZ1HS97sUTBD4GLH8W8VTbpT2lRj AllbI1RMSeRl/tdtnvziYJJLb2xLEwaJzrpeIMrc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730134AbfIDMwv (ORCPT ); Wed, 4 Sep 2019 08:52:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:39552 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727083AbfIDMwv (ORCPT ); Wed, 4 Sep 2019 08:52:51 -0400 Received: from tleilax.poochiereds.net (68-20-15-154.lightspeed.rlghnc.sbcglobal.net [68.20.15.154]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8B30F21883; Wed, 4 Sep 2019 12:52:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567601569; bh=XG+z6BHhOmv9W2OyuDcqw63mHyObz78oeswsmfEdF1U=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=QOvybiJzp85IlBNCfwgLsBnLV9DR4UQ+d3iO+92iuV9rSa0S6OBqWysT1ufEq9jPg Uc8pw3mW3WhdRGHShvIhIShiLbWPqR1oIpH89892Mb1phi9Lqta58kkyAJU+pCa6lo XwT3v0mpqc9uUS8Hbn+5AeFK7k62BlqLx2/zGjmo= Message-ID: <2227b44d9e36f9bd129c73ee77c03b35d023236a.camel@kernel.org> Subject: Re: [RFC PATCH v2 02/19] fs/locks: Add Exclusive flag to user Layout lease From: Jeff Layton To: Ira Weiny Cc: Dave Chinner , Andrew Morton , Jason Gunthorpe , Dan Williams , Matthew Wilcox , Jan Kara , Theodore Ts'o , John Hubbard , Michal Hocko , linux-xfs@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-ext4@vger.kernel.org, linux-mm@kvack.org Date: Wed, 04 Sep 2019 08:52:47 -0400 In-Reply-To: <20190829233408.GD18249@iweiny-DESK2.sc.intel.com> References: <20190809225833.6657-1-ira.weiny@intel.com> <20190809225833.6657-3-ira.weiny@intel.com> <20190814215630.GQ6129@dread.disaster.area> <20190829233408.GD18249@iweiny-DESK2.sc.intel.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.32.4 (3.32.4-1.fc30) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, 2019-08-29 at 16:34 -0700, Ira Weiny wrote: > Missed this. sorry. > > On Mon, Aug 26, 2019 at 06:41:07AM -0400, Jeff Layton wrote: > > On Thu, 2019-08-15 at 07:56 +1000, Dave Chinner wrote: > > > On Wed, Aug 14, 2019 at 10:15:06AM -0400, Jeff Layton wrote: > > > > On Fri, 2019-08-09 at 15:58 -0700, ira.weiny@intel.com wrote: > > > > > From: Ira Weiny > > > > > > > > > > Add an exclusive lease flag which indicates that the layout mechanism > > > > > can not be broken. > > > > > > > > > > Exclusive layout leases allow the file system to know that pages may be > > > > > GUP pined and that attempts to change the layout, ie truncate, should be > > > > > failed. > > > > > > > > > > A process which attempts to break it's own exclusive lease gets an > > > > > EDEADLOCK return to help determine that this is likely a programming bug > > > > > vs someone else holding a resource. > > > ..... > > > > > diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h > > > > > index baddd54f3031..88b175ceccbc 100644 > > > > > --- a/include/uapi/asm-generic/fcntl.h > > > > > +++ b/include/uapi/asm-generic/fcntl.h > > > > > @@ -176,6 +176,8 @@ struct f_owner_ex { > > > > > > > > > > #define F_LAYOUT 16 /* layout lease to allow longterm pins such as > > > > > RDMA */ > > > > > +#define F_EXCLUSIVE 32 /* layout lease is exclusive */ > > > > > + /* FIXME or shoudl this be F_EXLCK??? */ > > > > > > > > > > /* operations for bsd flock(), also used by the kernel implementation */ > > > > > #define LOCK_SH 1 /* shared lock */ > > > > > > > > This interface just seems weird to me. The existing F_*LCK values aren't > > > > really set up to be flags, but are enumerated values (even if there are > > > > some gaps on some arches). For instance, on parisc and sparc: > > > > > > I don't think we need to worry about this - the F_WRLCK version of > > > the layout lease should have these exclusive access semantics (i.e > > > other ops fail rather than block waiting for lease recall) and hence > > > the API shouldn't need a new flag to specify them. > > > > > > i.e. the primary difference between F_RDLCK and F_WRLCK layout > > > leases is that the F_RDLCK is a shared, co-operative lease model > > > where only delays in operations will be seen, while F_WRLCK is a > > > "guarantee exclusive access and I don't care what it breaks" > > > model... :) > > > > > > > Not exactly... > > > > F_WRLCK and F_RDLCK leases can both be broken, and will eventually time > > out if there is conflicting access. The F_EXCLUSIVE flag on the other > > hand is there to prevent any sort of lease break from > > Right EXCLUSIVE will not break for any reason. It will fail truncate and hole > punch as we discussed back in June. This is for the use case where the user > has handed this file/pages off to some hardware for which removing the lease > would be impossible. _And_ we don't anticipate any valid use case that someone > will need to truncate short of killing the process to free up file system > space. > > > I'm guessing what Ira really wants with the F_EXCLUSIVE flag is > > something akin to what happens when we set fl_break_time to 0 in the > > nfsd code. nfsd never wants the locks code to time out a lease of any > > sort, since it handles that timeout itself. > > > > If you're going to add this functionality, it'd be good to also convert > > knfsd to use it as well, so we don't end up with multiple ways to deal > > with that situation. > > Could you point me at the source for knfsd? I looked in > > git://git.linux-nfs.org/projects/steved/nfs-utils.git > > but I don't see anywhere leases are used in that source? > Ahh sorry that wasn't clear. It's the fs/nfsd directory in the Linux kernel sources. See nfsd4_layout_lm_break and nfsd_break_deleg_cb in particular. -- Jeff Layton